diff --git a/test/test_i18n_translator.rb b/test/test_i18n_translator.rb
new file mode 100644
index 0000000..3eb225c
--- /dev/null
+++ b/test/test_i18n_translator.rb
@@ -0,0 +1,82 @@
+require 'minitest/autorun'
+require 'prism'
+
+class I18nTranslatorTest < Minitest::Test
+  def setup
+    @backend = Prism::I18n::Backend.new
+    @backend.store_translations(:en, {
+      'greeting' => 'Hello, %{name}!',
+      'apples' => { 'zero' => 'no apples', 'one' => 'one apple', 'other' => '%{count} apples' },
+      'cars' => { 'one' => 'one car', 'other' => '%{count} cars' },
+      'nav' => { 'home' => 'Home' }
+    })
+    @backend.store_translations(:pl, 'nav' => { 'home' => 'Strona glowna' })
+    @translator = Prism::I18n::Translator.new(@backend, default_locale: :en)
+  end
+
+  def test_translate_plain_string
+    assert_equal 'Home', @translator.translate('nav.home', locale: :en)
+  end
+
+  def test_translate_interpolates_named_placeholders
+    assert_equal 'Hello, Ada!', @translator.translate('greeting', locale: :en, name: 'Ada')
+  end
+
+  def test_translate_missing_interpolation_argument_raises
+    assert_raises(Prism::I18n::Translator::MissingInterpolationError) do
+      @translator.translate('greeting', locale: :en)
+    end
+  end
+
+  def test_translate_missing_key_raises_by_default
+    assert_raises(Prism::I18n::Translator::MissingTranslationError) do
+      @translator.translate('nowhere.at.all', locale: :en)
+    end
+  end
+
+  def test_translate_missing_key_uses_default_when_given
+    assert_equal 'fallback text', @translator.translate('nowhere.at.all', locale: :en, default: 'fallback text')
+  end
+
+  def test_translate_pluralizes_zero_one_other
+    assert_equal 'no apples', @translator.translate('apples', locale: :en, count: 0)
+    assert_equal 'one apple', @translator.translate('apples', locale: :en, count: 1)
+    assert_equal '5 apples', @translator.translate('apples', locale: :en, count: 5)
+  end
+
+  def test_translate_pluralizes_zero_as_other_when_no_zero_key
+    assert_equal '0 cars', @translator.translate('cars', locale: :en, count: 0)
+  end
+
+  def test_translate_falls_back_to_default_locale_for_missing_key_in_requested_locale
+    assert_equal 'Hello, Ada!', @translator.translate('greeting', locale: :pl, name: 'Ada')
+  end
+
+  def test_translate_prefers_requested_locale_over_fallback
+    assert_equal 'Strona glowna', @translator.translate('nav.home', locale: :pl)
+  end
+
+  def test_custom_fallback_chain_is_tried_before_default_locale
+    backend = Prism::I18n::Backend.new
+    backend.store_translations(:en, 'only_en' => 'English only')
+    backend.store_translations(:'pt-BR', 'greeting' => 'Ola')
+    translator = Prism::I18n::Translator.new(backend, default_locale: :en, fallbacks: { pt: [:'pt-BR'] })
+    assert_equal 'Ola', translator.translate('greeting', locale: :pt)
+  end
+
+  def test_localize_time_with_default_format
+    time = Time.utc(2026, 3, 5, 8, 30, 0)
+    assert_equal '2026-03-05 08:30:00', @translator.localize(time, locale: :en)
+  end
+
+  def test_localize_date_with_default_format
+    date = Date.new(2026, 3, 5)
+    assert_equal '2026-03-05', @translator.localize(date, locale: :en)
+  end
+
+  def test_localize_uses_named_format_from_backend
+    @backend.store_translations(:en, 'time' => { 'formats' => { 'short' => '%d.%m.%Y' } })
+    time = Time.utc(2026, 3, 5, 8, 30, 0)
+    assert_equal '05.03.2026', @translator.localize(time, locale: :en, format: :short)
+  end
+end